Question

In an ideal op-amp, which is not true?

• A. Open loop voltage gain is infinite
• B. Input resistance is infinite
• C. Slew rate is infinite
• D. CMRR is zero

Hint:

Ideal Op-Amp Assumptions. Gain \(\to \infty\), \(R_{in \to \infty\), \(R_{out \to 0\), BW \(\to \infty\), Slew Rate \(\to \infty\), CMRR \(\to \infty\). Remember CMRR is infinite for perfect common-mode rejection.

Answer 1

The Correct Option is D

The characteristics assumed for an ideal operational amplifier include: - Infinite open-loop voltage gain (\(A_{OL} = \infty\))
- Infinite input resistance (\(R_{in} = \infty\)), meaning zero input current
- Zero output resistance (\(R_{out} = 0\))
- Infinite bandwidth (\(BW = \infty\))
- Infinite Slew Rate (\(SR = \infty\)), meaning the output can change instantly
- Infinite Common-Mode Rejection Ratio (\(CMRR = \infty\)), meaning it perfectly rejects signals common to both inputs
- Zero input offset voltage and current
Statement (4) says CMRR is zero
For an ideal op-amp, CMRR is infinite
Therefore, statement (4) is not true for an ideal op-amp